No. 583] . BOLE OF ENVIRONMENT IN DBOSOPIIILA 



medium) was made more acid (and liquid) by adding an 

 equal amount of a 5 per cent, solution of acetic acid. 

 Other food was made alkaline by adding dry sodium 

 bicarbonate, or a 1 per cent, solution of sodium hy- 

 droxide. The acid food gave very abnormal flies; the 

 alkaline food was difficult to control as the flies refused 

 in most cases to lay eggs on it, if it remained alkaline, 

 and the food often dried up, or putritied, or grew mouldy. 

 Moreover, the highly alkaline food often became acid 

 over night owing to fermentation changes taking place 

 within the pieces of fruit used for food. But several 

 times good results were obtained with cultures that had 

 been strictly neutral and often alkaline throughout the 

 time of the experiment and from these the flies were ab- 

 normal. Omitting all details it may be stated that an 

 acid or alkaline (neutral) condition as such is not the 

 cause that conditions the character. 



3. Food of Parents.— At one time it seemed possible 

 that the kind of food that the female was supplied with 

 might for a time continue to affect her eggs, even al- 

 though the parent was transferred to a medium that 

 acted in the opposite direction. Careful tests showed 

 conclusively that such was not the case. Some of the 

 evidence for this statement will be given later. 



4. Egg versus Sperm. — Heterozygous females may be 

 produced either by using a normal female and abnormal 

 male, or conversely an abnormal female and a normal 

 male. Certain cultures seemed, at one time, to show that 

 when the egg parent was abnormal the offspring were 

 more abnormal than when the egg parent was normal, 

 but careful tests disproved this view. The difference in 

 the cultures, that led to the suspicion mentioned, was due 

 to the large number of eggs laid by the normal females, 

 hence greater crowding and more rapid disappearance 

 of the moist food. 



5. Influence of Genetic Factors.— Certain mutant stocks, 

 notably black, seemed at times to show the abnormality 

 less strongly than other stocks, but here, as in the last 



